Method for printing three-dimensional parts wtih crystallization kinetics control

ABSTRACT

A method for printing a three-dimensional part with an additive manufacturing system, which includes providing a part material that compositionally has one or more semi-crystalline polymers and one or more secondary materials that are configured to retard crystallization of the one or more semi-crystalline polymers, where the one or more secondary materials are substantially miscible with the one or more semi-crystalline polymers. The method also includes melting the part material in the additive manufacturing system, forming at least a portion of a layer of the three-dimensional part from the melted part material in a build environment, and maintaining the build environment at an annealing temperature that is between a glass transition temperature of the part material and a cold crystallization temperature of the part material.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 13/833,526, filed Mar. 15, 2013, which claimspriority to U.S. Provisional Patent Application No. 61/729,043, filed onNov. 21, 2012 and the present application also claims priority to U.S.Provisional Application No. 61/909,611, entitled “METHOD FOR PRINTINGTHREE-DIMENSIONAL PARTS WITH CRYSTALLIZATION KINETICS CONTROL”, andfiled on Nov. 27, 2013, the contents of which are hereby incorporated intheir entirety.

BACKGROUND

The present disclosure relates to additive manufacturing techniques forprinting three-dimensional (3D) parts. In particular, the presentdisclosure relates to additive manufacturing methods for printing 3Dparts in a layer-by-layer manner from part materials having one or moresemi-crystalline polymeric materials.

Additive manufacturing systems are used to print or otherwise build 3Dparts from digital representations of the 3D parts (e.g., AMF and STLformat files) using one or more additive manufacturing techniques.Examples of commercially available additive manufacturing techniquesinclude extrusion-based techniques, jetting, selective laser sintering,powder/binder jetting, electron-beam melting, and stereolithographicprocesses. For each of these techniques, the digital representation ofthe 3D part is initially sliced into multiple horizontal layers. Foreach sliced layer, a tool path is then generated, which providesinstructions for the particular additive manufacturing system to printthe given layer.

For example, in an extrusion-based additive manufacturing system, a 3Dpart may be printed from a digital representation of the 3D part in alayer-by-layer manner by extruding a flowable part material. The partmaterial is extruded through an extrusion tip carried by a print head ofthe system, and is deposited as a sequence of roads on a substrate in anx-y plane. The extruded part material fuses to previously deposited partmaterial, and solidifies upon a drop in temperature. The position of theprint head relative to the substrate is then incremented along a z-axis(perpendicular to the x-y plane), and the process is then repeated toform a 3D part resembling the digital representation.

In fabricating 3D parts by depositing layers of a part material,supporting layers or structures are typically built underneathoverhanging portions or in cavities of 3D parts under construction,which are not supported by the part material itself. A support structuremay be built utilizing the same deposition techniques by which the partmaterial is deposited. The host computer generates additional geometryacting as a support structure for the overhanging or free-space segmentsof the 3D part being formed. Support material is then deposited from asecond nozzle pursuant to the generated geometry during the printingprocess. The support material adheres to the part material duringfabrication, and is removable from the completed 3D part when theprinting process is complete.

SUMMARY

An aspect of the present disclosure is directed to a method for printinga 3D part with an additive manufacturing system. The method includesproviding a part material that compositionally includes one or moresemi-crystalline polymers and one or more secondary materials that areconfigured to retard crystallization of the one or more semi-crystallinepolymers, where the one or more secondary materials are substantiallymiscible with the one or more semi-crystalline polymers. The method alsoincludes melting the part material in the additive manufacturing system,forming at least a portion of a layer of the 3D part from the meltedpart material in a build environment, and maintaining the buildenvironment at an annealing temperature that is between a glasstransition temperature of the part material and a cold crystallizationtemperature of the part material.

Another aspect of the present disclosure is directed to a method forprinting a 3D part from with an additive manufacturing system, where themethod includes providing a part material that compositionally comprisesone or more semi-crystalline polymers and one or more amorphous polymersthat are substantially miscible with the one or more semi-crystallinepolymers. The method also includes maintaining a build environment ofthe additive manufacturing system, at least in a deposition region ofthe build environment, at an annealing temperature that is between aglass transition temperature of the part material and a coldcrystallization temperature of the part material. The method alsoincludes feeding the part material to a print head retained by of theadditive manufacturing system, melting the part material in the printhead, extruding the melted part material from the print head, anddepositing the extruded part material onto a build surface in thedeposition region to form at least a portion of a layer of the 3D partfrom the extruded part material.

Another aspect of the present disclosure is directed to a method forprinting a 3D part from with an additive manufacturing system, where themethod includes providing a part material that compositionally comprisesone or more semi-crystalline polymers and one or more amorphous polymersthat are substantially miscible with the one or more semi-crystallinepolymers. The method also includes melting the part material in theadditive manufacturing system, forming layers of the three-dimensionalpart from the melted part material using an additive manufacturingtechnique, wherein the layers are formed in a region that is maintainedat an annealing temperature that is similar to a glass transitiontemperature of the part material (e.g., within about 10° C.), andreheating the printed three-dimensional part to one or more temperaturesthat are within a small range of a cold crystallization temperature ofthe part material (e.g., within about 10° C.).

Another aspect of the present disclosure is directed to a method forprinting a 3D part from with a selective laser sintering system. Themethod includes providing a part material that compositionally comprisesone or more semi-crystalline polymers and one or more amorphous polymersthat are substantially miscible with the one or more semi-crystallinepolymers. The methods also includes forming layers of the 3D part fromthe part material using the selective laser sintering system, andmaintaining an environmental temperature for the formed layers that isbetween a hot crystallization temperature of the part material and amelting temperature of the part material.

DEFINITIONS

Unless otherwise specified, the following terms as used herein have themeanings provided below:

The term “polymer” refers to a polymeric material having one or moremonomer species, including homopolymers, copolymers, terpolymers, andthe like.

The term “semi-crystalline polymer” refers to a polymer capable ofexhibiting an average percent crystallinity in a solid state of at leastabout 10% by weight when allowed to crystallize to its fullest extent.The term “semi-crystalline polymer” includes polymeric materials capableof having crystallinities up to 100% (i.e., fully-crystalline polymericmaterials). The term “amorphous polymer” refers to a polymer that is nota semi-crystalline polymer.

Reference to “a” chemical compound refers one or more molecules of thechemical compound, rather than being limited to a single molecule of thechemical compound. Furthermore, the one or more molecules may or may notbe identical, so long as they fall under the category of the chemicalcompound. Thus, for example, “a” polyamide is interpreted to include oneor more polymer molecules of the polyamide, where the polymer moleculesmay or may not be identical (e.g., different molecular weights and/orisomers).

The terms “at least one” and “one or more of” an element are usedinterchangeably, and have the same meaning that includes a singleelement and a plurality of the elements, and may also be represented bythe suffix “(s)” at the end of the element. For example, “at least onepolyamide”, “one or more polyamides”, and “polyamide(s)” may be usedinterchangeably and have the same meaning.

Directional orientations such as “above”, “below”, “top”, “bottom”, andthe like are made with reference to a layer-printing direction of a 3Dpart. In the embodiments shown below, the layer-printing direction isthe upward direction along the vertical z-axis. In these embodiments,the terms “above”, “below”, “top”, “bottom”, and the like are based onthe vertical z-axis. However, in embodiments in which the layers of 3Dparts are printed along a different axis, such as along a horizontalx-axis or y-axis, the terms “above”, “below”, “top”, “bottom”, and thelike are relative to the given axis.

Unless otherwise specified, characteristics of a material or a 3D partprinted from the material refer to the characteristics as measuredparallel to the orientation of the 3D part layers and perpendicular tothe layer-printing direction, and is referred to as an “xy-direction”.Correspondingly, the term “z-direction”, with reference tocharacteristics of a material or a 3D part printed from the materialrefer to the characteristics as measured perpendicular to theorientation of the 3D part layers and parallel to the layer-printingdirection. Unless the measurement direction is specified as “in thez-direction”, a measurement referred to herein is taken in thexy-direction. For example, a tensile strength of a 3D part of 10,000 psirefers to a tensile strength measured parallel to the layers of the 3Dpart. Alternatively, a tensile strength of a 3D part in the z-directionof 8,000 psi refers to a tensile strength measured perpendicular to thelayers of the 3D part.

Unless otherwise specified, temperatures referred to herein are based onatmospheric pressure (i.e. one atmosphere).

The term “additive manufacturing system” refers to a system that prints,builds, or otherwise produces 3D parts and/or support structures atleast in part using an additive manufacturing technique. The additivemanufacturing system may be a stand-alone unit, a sub-unit of a largersystem or production line, and/or may include other non-additivemanufacturing features, such as subtractive-manufacturing features,pick-and-place features, two-dimensional printing features, and thelike.

The term “providing”, such as for “providing a consumable material”,when recited in the claims, is not intended to require any particulardelivery or receipt of the provided item. Rather, the term “providing”is merely used to recite items that will be referred to in subsequentelements of the claim(s), for purposes of clarity and ease ofreadability.

The terms “preferred” and “preferably” refer to embodiments of theinvention that may afford certain benefits, under certain circumstances.However, other embodiments may also be preferred, under the same orother circumstances. Furthermore, the recitation of one or morepreferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the present disclosure.

The terms “about” and “substantially” are used herein with respect tomeasurable values and ranges due to expected variations known to thoseskilled in the art (e.g., limitations and variabilities inmeasurements).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an additive manufacturing system configured toprint 3D parts pursuant to the method of the present disclosure.

FIG. 2 is a front view of a print head of the additive manufacturingsystem.

FIG. 3 is an expanded sectional view of a drive mechanism, a liquefierassembly, and a nozzle of the print head.

FIG. 4 is an illustrative differential scanning calorimetry (DSC) plotof heat flow versus temperature for a part material.

FIG. 5 is a photograph of printed 3D parts and pellets from a PEEK/PEIpart material.

FIG. 6 is a graphical illustration of modulus versus temperature forexample PET part materials printed in heated chambers having differentannealing temperatures.

FIG. 7 is a graphical illustration of the tan-delta results for theexample PET part materials shown in FIG. 6.

FIG. 8 is a graphical illustration of modulus versus temperature forexample PET part materials, illustrating crystallization effects of apost-printing crystallization process.

DETAILED DESCRIPTION

The present disclosure is directed to an additive manufacturing methodfor printing 3D parts in a layer-by-layer manner from a part materialthat, in a preferred embodiment, compositionally includes a blend of oneor more semi-crystalline polymers and one or more secondary materialsthat retard crystallization of the semi-crystalline polymer(s), such asone or more amorphous polymers that are at least partially miscible withthe semi-crystalline polymer(s). In particular, the method involvescontrolling the crystallization kinetics of the semi-crystallinepolymer(s) upon cooling from a melted state to minimize or otherwisereduce the percent crystallinity of the printed part material, whilealso generating enough crystallization-exothermic energy to inducemolecular reptation at the extrudate-part interface.

As discussed below, the manner in which the crystallization kinetics ofthe part material are controlled can vary depending on the additivemanufacturing technique used, such as an extrusion-based additivemanufacturing technique, an electrophotography-based additivemanufacturing technique, or a selective laser sintering technique. Thesedistinctions are primarily due to the different thermal states in whichthe printed layers are typically held for the given additivemanufacturing techniques. As such, the following discussion initiallyfocuses on controlling the crystallization kinetics in anextrusion-based additive manufacturing system, and the applications foruse in an electrophotography-based additive manufacturing and aselective laser sintering system will be subsequently discussed.

Extrusion-based additive manufacturing systems typically print orotherwise build 3D parts from amorphous polymeric materials, such asacrylonitrile-butadiene-styrene (ABS) resins and polycarbonate resins.During a printing operation, the amorphous polymeric material is meltedand extruded as a series of roads, which cool down to form layers of a3D part. Due to the layer-by-layer nature of the printing, the coolingof each successive layer generates residual stresses in the 3D part,which are a function of the coefficient of thermal expansion, percentshrinkage, and tensile modulus of the material. If not relieved, theresidual stresses may physically distort the 3D part, such as by causingthe edges and corners of the 3D part to curl up, referred to as “curl”or “curling”.

Amorphous polymeric materials have little or no ordered arrangements oftheir polymer chains in their solid states. As such, these materialsexhibit glass transition effects that can be controlled to partiallyrelieve residual stresses. For example, as disclosed in Batchelder, U.S.Pat. No. 5,866,058, an amorphous polymeric material may be depositedinto a heated chamber (or at least a locally-heat deposition region)maintained at a temperature that is between a solidification temperatureand a glass transition temperature of the material. This anneals thesuccessively-printed printed layers, allowing them to cool down andsolidify slowly, which can partially relieve the residual stresses.

Semi-crystalline polymeric materials, however, have different mechanicaland thermal characteristics from amorphous polymeric materials. Forexample, due to their achievable crystallinity, 3D parts printed withsemi-crystalline polymeric materials may exhibit superior mechanicalproperties compared to 3D parts printed with amorphous polymericmaterials. However, due to their higher levels of achievablecrystallinity, semi-crystalline polymeric materials can exhibitdiscontinuous changes in volume upon solidification. Therefore, layersof a semi-crystalline polymeric material may contract and shrink whendeposited, thereby accumulating residual stresses.

In comparison to amorphous polymeric materials, which can haverelatively broad annealing windows, it has been conventionally difficultto maintain a temperature window that is suitable for annealingsemi-crystalline polymers, particularly with extrusion-based additivemanufacturing systems. For instance, curl will result if we hold thepolymer above the window, as will curl result if below the window. Anyvariations outside of this small temperature window will result insolidification with discontinuous changes in volume, such as curl, ifabove or below the temperature window. The discontinuous changes involume can be particularly troublesome for extrusion-based additivemanufacturing systems where the printed 3D parts or support structuresare coupled to underlying and non-shrinkable build sheets. Furthermore,sagging may occur if there is not enough crystallinity generated duringthe cooling process. Each of these conditions may result in distortionsof the printed 3D part. As such, it has been difficult to printdimensionally stable 3D parts from semi-crystalline polymers usingextrusion-based additive manufacturing systems, where the amount ofcrystallinity formed during the cooling process is sufficient such thatthe 3D parts do not sag, yet also do not induce curl forces that willcurl the 3D part.

However, as discussed below, the crystallization kinetics of particularpart materials can be controlled in an extrusion-based additivemanufacturing system to print 3D parts having mechanical properties(e.g., strengths and ductilities) similar to those of semi-crystallinepolymeric materials, while also being annealable in a heated chamber ofan additive manufacturing system (or at least a locally-heateddeposition region) to partially relieve residual stresses.

FIGS. 1-3 illustrate system 10, which is an example extrusion-basedadditive manufacturing system for printing or otherwise building 3Dparts, from the part material blends discussed herein, in a manner thatcontrols the crystallization kinetics, as discussed below. Suitableextrusion-based additive manufacturing systems for system 10 includefused deposition modeling systems developed by Stratasys, Inc., EdenPrairie, Minn. under the trademark “FDM”.

As shown in FIG. 1, system 10 may include chamber 12, platen 14, platengantry 16, print head 18, head gantry 20, and consumable assemblies 22and 24. Chamber 12 is an example enclosed build environment thatcontains platen 14 for printing 3D parts and support structures, wherechamber 12 may be may be optionally omitted and/or replaced withdifferent types of build environments. For example, a 3D part andsupport structure may be built in a build environment that is open toambient conditions or may be enclosed with alternative structures (e.g.,flexible curtains).

In the shown example, the interior volume of chamber 12 may be heatedwith heater 12 h to reduce the rate at which the part and supportmaterials solidify after being extruded and deposited (e.g., to reducedistortions and curling). Heater 12 h may be any suitable device orassembly for heating the interior volume of chamber 12, such as byradiant heating and/or by circulating heated air or other gas (e.g.,inert gases). In alternative embodiments, heater 12 h may be replacedwith other conditioning devices, such as a cooling unit to generate andcirculate cooling air or other gas. The particular thermal conditionsfor the build environment may vary depending on the particularconsumable materials used.

In further embodiments, the heating may be localized rather than in anentire chamber 12. For example, the deposition region may be heated in alocalized manner. Example techniques for locally-heating a depositionregion include heating platen 14 and/or with directing heat air jetstowards platen 14 and/or the 3D parts/support structures being printed).As discussed above, the heating in chamber 12 and/or the localizeddeposition region anneals the printed layers of the 3D parts (andsupport structures) to partially relieve the residual stresses, therebyreducing curling of the 3D parts.

Platen 14 is a platform on which 3D parts and support structures areprinted in a layer-by-layer manner. In some embodiments, platen 14 mayalso include a flexible polymeric film or liner on which the 3D partsand support structures are printed. In the shown example, print head 18is a dual-tip extrusion head configured to receive consumable filamentsfrom consumable assemblies 22 and 24 (e.g., via guide tubes 26 and 28)for printing 3D part 30 and support structure 32 on platen 14.Consumable assembly 22 may contain a supply of the part material forprinting 3D part 30 from the part material. Consumable assembly 24 maycontain a supply of a support material for printing support structure 32from the given support material.

Platen 14 is supported by platen gantry 16, which is a gantry assemblyconfigured to move platen 14 along (or substantially along) a verticalz-axis. Correspondingly, print head 18 is supported by head gantry 20,which is a gantry assembly configured to move print head 18 in (orsubstantially in) a horizontal x-y plane above chamber 12.

In an alternative embodiment, platen 14 may be configured to move in thehorizontal x-y plane within chamber 12, and print head 18 may beconfigured to move along the z-axis. Other similar arrangements may alsobe used such that one or both of platen 14 and print head 18 aremoveable relative to each other. Platen 14 and print head 18 may also beoriented along different axes. For example, platen 14 may be orientedvertically and print head 18 may print 3D part 30 and support structure32 along the x-axis or the y-axis.

System 10 also includes controller 34, which is one or more controlcircuits configured to monitor and operate the components of system 10.For example, one or more of the control functions performed bycontroller 34 can be implemented in hardware, software, firmware, andthe like, or a combination thereof. Controller 34 may communicate overcommunication line 36 with chamber 12 (e.g., with a heating unit forchamber 12), print head 18, and various sensors, calibration devices,display devices, and/or user input devices.

In some embodiments, controller 34 may also communicate with one or moreof platen 14, platen gantry 16, head gantry 20, and any other suitablecomponent of system 10. While illustrated as a single signal line,communication line 36 may include one or more electrical, optical,and/or wireless signal lines, allowing controller 34 to communicate withvarious components of system 10. Furthermore, while illustrated outsideof system 10, controller 34 and communication line 36 may be internalcomponents to system 10.

System 12 and/or controller 34 may also communicate with computer 38,which is one or more computer-based systems that communicates withsystem 12 and/or controller 34, and may be separate from system 12, oralternatively may be an internal component of system 12. Computer 38includes computer-based hardware, such as data storage devices,processors, memory modules and the like for generating and storing toolpath and related printing instructions. Computer 38 may transmit theseinstructions to system 10 (e.g., to controller 34) to perform printingoperations. Controller 34 and computer 38 may collectively be referredto as a controller assembly for system 10.

FIG. 2 illustrates a suitable device for print head 18, as described inLeavitt, U.S. Pat. No. 7,625,200. Additional examples of suitabledevices for print head 18, and the connections between print head 18 andhead gantry 20 include those disclosed in Crump et al., U.S. Pat. No.5,503,785; Swanson et al., U.S. Pat. No. 6,004,124; LaBossiere, et al.,U.S. Pat. Nos. 7,384,255 and 7,604,470; Batchelder et al., U.S. Pat. No.7,896,209; and Comb et al., U.S. Pat. No. 8,153,182. In additionalembodiments, in which print head 18 is an interchangeable, single-nozzleprint head, examples of suitable devices for each print head 18, and theconnections between print head 18 and head gantry 20 include thosedisclosed in Swanson et al., U.S. Patent Application Publication No.2012/0164256.

In the shown dual-tip embodiment, print head 18 includes two drivemechanism 40 and 42, two liquefier assemblies 44 and 46, and two nozzles48 and 50. In this embodiment the part material and the support materialeach preferably have a filament geometry for use with print head 18. Forexample, as best shown in FIG. 3, the part material may be provided asfilament 52. In alternative embodiments, the part material of thepresent disclosure may be provided in powder or pellet form for use inan auger-pump print head, such as disclosed in Bosveld et al., U.S.Publication No. 2013/0333798.

During operation, controller 34 may direct wheels 54 of drive mechanism40 to selectively draw successive segments filament 52 from consumableassembly 22 (via guide tube 26), and feed filament 52 to liquefierassembly 44. Liquefier assembly 44 may include liquefier tube 56,thermal block 58, heat shield 60, and tip shield 62, where liquefiertube 56 includes inlet end 64 for receiving the fed filament 52. Nozzle48 and tip shield 62 are accordingly secured to outlet end 66 ofliquefier tube 56, and liquefier tube 56 extends through thermal block58 and heat shield 60.

While liquefier assembly 44 is in its active state, thermal block 58heats liquefier tube 56 to define heating zone 68. The heating ofliquefier tube 56 at heating zone 68 melts the part material of filament52 in liquefier tube 56 to form melt 70. The upper region of liquefiertube 56 above heating zone 68, referred to as transition zone 72, is notdirectly heated by thermal block 58. This generates a thermal gradientor profile along the longitudinal length of liquefier tube 56.

The molten portion of the part material (i.e., melt 70) forms meniscus74 around the unmelted portion of filament 52. During an extrusion ofmelt 70 through nozzle 48, the downward movement of filament 52functions as a viscosity pump to extrude the part material of melt 70out of nozzle 48 as extruded roads to print 3D part 30 in alayer-by-layer manner. While thermal block 58 heats liquefier tube 56 atheating zone 68, cooling air may also be blown through a manifold 76toward inlet end 64 of liquefier tube 56, as depicted by arrows 78. Heatshield 60 assists in directing the air flow toward inlet end 64. Thecooling air reduces the temperature of liquefier tube 56 at inlet end64, which prevents filament 52 from softening or melting at transitionzone 72.

In some embodiments, controller 34 may servo or swap liquefierassemblies 44 and 46 between opposing active and stand-by states. Forexample, while liquefier assembly 46 is served to its active state forextruding the support material to print a layer of support structure 32,liquefier assembly 44 is switched to a stand-by state to prevent thepart material from being extruded while liquefier assembly 46 is beingused. After a given layer of the support material is completed,controller 34 then serves liquefier assembly 46 to its stand-by state,and switches liquefier assembly 44 to its active state for extruding thepart material to print a layer of 3D part 30. This servo process may berepeated for each printed layer until 3D part 30 and support structure32 are completed.

While liquefier assembly 46 is in its active state for printing supportstructure 32 from a support material filament, drive mechanism 42,liquefier assembly 46, and nozzle 50 (each shown in FIG. 2) may operatein the same manner as drive mechanism 40, liquefier assembly 44, andnozzle 48 for extruding the support material. In particular, drivemechanism 40 may draw successive segments of the support materialfilament from consumable assembly 24 (via guide tube 28), and feed thesupport material filament to liquefier assembly 46. Liquefier assembly46 thermally melts the successive segments of the received supportmaterial filament such that it becomes a molten support material. Themolten support material may then be extruded and deposited from nozzle50 as a series of roads onto platen 14 for printing support structure 32in a layer-by-layer manner in coordination with the printing of 3D part30.

As mentioned above, the part material compositionally includes a blendof one or more semi-crystalline polymers and one or more secondarymaterials that retard crystallization of the semi-crystallinepolymer(s). Preferably, the secondary material(s) include one or moreamorphous polymers that are at least partially miscible with thesemi-crystalline polymer(s). The following discussion is made withreference to the secondary material(s) as amorphous polymer(s) with theunderstanding that the part material may alternatively include othernon-amorphous polymer(s) to retard crystallization of thesemi-crystalline polymer(s). Nonetheless, amorphous polymer(s) arepreferred as they may also provide additional desired characteristics tothe part material.

More preferably, the semi-crystalline polymer(s) and the amorphouspolymer(s) are substantially miscible with each other. The substantiallymiscible blend may exhibit a co-continuous phase of the semi-crystallinepolymer(s) and the amorphous polymer(s), or more preferably a singlecontinuous phase of the semi-crystalline polymer(s) and the amorphouspolymer(s). While not wishing to be bound by theory, it is believed thatthis miscibility allows the amorphous polymer(s) to physically impedethe semi-crystalline polymer(s) from forming crystalline regions, whichaccordingly retards crystallization.

In some embodiments, the amorphous polymer(s) of the part material havesubstantially no measurable melting points (less than 5 calories/gram)using differential scanning calorimetry (DSC) pursuant to ASTM D3418-08.Correspondingly, in these embodiments, the semi-crystalline polymer(s)of the part material have measureable melting points (5 calories/gram ormore) using DSC pursuant to ASTM D3418-08. As discussed below, the partmaterial may also optionally include one or more additives dispersed inthe blend.

FIG. 4 illustrates a DSC plot for an exemplary part material of thepresent disclosure having a substantially miscible blend of one or moresemi-crystalline polymers and one or more amorphous polymers. The DSCpot in FIG. 4 shows the various thermal transitions that the partmaterial may exhibit. For example, during an initial heating phase, suchas when the part material is melted in liquefier assembly 44, the partmaterial may produce a heating profile 80 with a glass transitiontemperature (T_(g)), a cold crystallization temperature (T_(c,cold)),and a melting temperature (T_(m)). The glass transition temperature(T_(g)) refers to the point along curve 80 where the part materialundergoes a second-order transition to achieve an increase in its heatcapacity.

In some embodiments, the semi-crystalline copolymer or blend may consistessentially of semi-crystalline polymers that exhibit substantial orcomplete miscibility. This may be the case for closely related polymersthat are synthesized using (i) one or more base monomers, and (ii) asizable fraction of one or more monomers that are structural or opticalisomers of the base monomer(s) usually used in the synthesis. Otheroptions include additional, unrelated monomers added in sufficientamounts to substantially alter the glass transition temperature,crystallization temperatures, re-crystallization temperatures, meltingpoints, and/or enthalpies of fusion, as measured during heating orcooling at a specified, constant rate.

Examples of some suitable techniques for these embodiments includecontrolling the level of d-lactide and l-lactide incorporated into afinal polylactic acid polymer to achieve a poly-DL-lactide. The DLpolylactic acid copolymer has slower crystallization kinetics and mayeven exhibit characteristics of a completely amorphous polymer.

Another useful example includes polyetherketoneketone (PEKK).Crystallinity, melting, point, enthalpy of fusion, crystallization rate,and even glass transition temperature have been seen to drop as theratio of terephthalic moieties-to-isophtalic moieties in the copolymerbackbone increases. In PEKK, an observed range from highly crystallineto practically amorphous behavior is observed interephthalic-to-isophtalic moiety ratios from about 80/20 to about60/40.

A third useful example includes the synthesis of polyesters,specifically those based on a poly(ethyleneterephthalate) polymer. Inthis case, some isophthalic moeities may be used in place of aterephthalic moeities to impart similar adjustments in crystallinity andcrystallization behavior as discussed above for PEKK. Additionally, oneor more glycols may be exchanged with one or more ethylene glycols,propylene glycols, and/or butylene glycols, such ascyclohexanedimethanol, for example, to achieve similar effects.

The cold crystallization temperature T_(c,cold) typically occurs due tothe increased mobility of the polymer molecules after exceeding theglass transition temperature T_(g), which allows a portion of thesemi-crystalline polymer(s) to form crystalline regions. Because thecrystallization is an exothermic process, it releases thermal energybased on a first-order transition, as illustrated by the inverted peakin heating profile 80.

The melting temperature T_(m) is the temperature at which the partmaterial fully liquefies, also based on a first-order transition.Typically, the part material is quickly heated past its meltingtemperature T_(m) in liquefier assembly 44 for extrusion. As such,during this point in the process, the glass transition temperature T_(g)and the cold crystallization temperature T_(c,cold) are not overlyrelevant to the crystallization state of the extrudate, other than forpotential melt flow and temperature control aspects in liquefierassembly 44.

The DSC plot in FIG. 4 also includes a cooling profile 82, whichillustrates hot crystallization temperature T_(c,hot), and describes thecrystallization kinetics of the part material as it cools down from itsmelting temperature T_(m). For example, after being extruded from nozzle48, the extruded part material may deposit as roads onto thepreviously-formed layer of 3D part 30, and begin cooling down. In otherwords, the part material begins to follow cooling profile 82 at acooling rate that depends on the environment temperature that 3D part 30is printed in (e.g. in chamber 12), as well as the particularcomposition of the part material and the size of 3D part 30.

Preferably, the layers of 3D part 30 are printed in chamber 12 (or atleast in a locally-heated deposition region) that is maintained at atemperature between a solidification temperature and the coldcrystallization temperature T_(c,cold) of the part material. This cananneal the successively-printed printed layers, allowing them to cooldown and solidify slowly, which can partially relieve the residualstresses.

In some embodiments, chamber 12 or the locally-heated deposition regionis maintained at a temperature between a solidification temperature andthe glass transition temperature T_(g) of the part material. Theseembodiments are suitable for part materials having low levels ofcrystalline regions, where the crystalline regions are not capable ofsupporting the printed layers at higher temperatures without slumping.

Alternatively, in other embodiments, chamber 12 or the locally-heateddeposition region is maintained at a temperature within an annealingwindow 84 having a lower limit at about the glass transition temperatureT_(g) of the part material and an upper limit that is less than the coldcrystallization temperature T_(c,cold) of the part material. Inparticular, annealing window 84 preferably encompasses the plateauregion 86 of DSC heating curve 80, which is above the increased slopefor the glass transition temperature T_(g) and below the decreased slopefor the cold crystallization temperature T_(c,cold). These embodimentsare suitable for part materials having enough crystalline regions tosupport the printed layers without slumping, despite being held abovethe glass transition temperature T_(g) of the part material.

In further embodiments, such as for use with low-temperature materials(e.g., those with glass transition temperatures near ambienttemperatures), chamber 12 may be omitted, and the part material may beprinted at room temperature (e.g., 25° C.). Regardless of the annealingtemperature, it has been found that the substantially-miscible blendsfor the part material modify the glass transition temperature T_(g) ofthe part material from that of the amorphous polymer(s), typicallyflowing the Flory-Fox Equation. The substantially-miscible blends mayalso decrease the hot crystallization temperature T_(c,hot) of the partmaterial from that of the pure semi-crystalline polymer(s). Thisprovides a unique advantage in that the cumulative amount ofcrystallization for the part material upon cooling can be reduced, whichaccordingly allows the printed layers of the part material to have lowlevels of crystallinity.

In particular, upon being extruded and deposited from nozzle 48, thepart material preferably is quickly cooled down past its hotcrystallization temperature T_(c,hot) to its annealing temperature belowthe cold crystallization temperature T_(c,cold) of the part material(e.g., within annealing window 84). This effectively supercools the partmaterial down below its cold crystallization temperature T_(c,cold).

It has been found that the level of crystallinity can be controlledbased on the particular annealing temperature used. For instance, ifmore amorphous properties are desired, the annealing temperature may beset to be set within about 5° C. of the glass transition temperatureT_(g) of the part material. Alternatively, if more crystallineproperties are desired, the annealing temperature may be set to be setwithin 5° C. of the cold crystallization temperature T_(c,cold) of thepart material. Furthermore, any intermediate amorphous-crystallinevariation may be achieved by maintaining the annealing temperature at aselected temperature within annealing window 84.

The incorporation of the amorphous polymer(s) also assists in physicallyimpeding the semi-crystalline polymer(s) from grouping together inordered arrangements to form crystalline regions. As such, as the partmaterial quickly cools down from its melting temperature T_(m), theshort residence time in the region between its hot crystallizationtemperature T_(c,hot) and its cold crystallization temperatureT_(c,cold), combined with the crystallization impedance, preferablyminimizes or otherwise reduces the formation of crystalline regions inthe part material.

For instance, if a given pure semi-crystalline polymer (i.e., non-blend)is capable of crystallizing to its fullest extent in about 3 seconds inthe region between its hot crystallization temperature T_(c,hot) and itscold crystallization temperature T_(c,cold), and if it quickly coolsdown such that it resides in this region for about one second, it mayform about one-third of is achievable of crystalline regions. Incomparison, the crystallization impedance of the part material blend mayrequire more than a 10 to 20-fold increase in the time required to fullycrystallize. As such, when the part material resides in this regionbetween its hot crystallization temperature T_(c,hot) and its coldcrystallization temperature T_(c,cold) for about one second, it may onlyform about 1-3% of its fully-achievable crystallinity, for example. Infact, it has been observed that the supercooled part material exhibits atranslucent, substantially non-opaque appearance. This is an indicationthat crystallinity has been significantly retarded since crystallineregions typically modify the indices of refraction of the extrudedlayers to render them opaque.

The minimized or reduced crystallization correspondingly reduces thediscontinuous changes in volume of the semi-crystalline polymer(s),thereby reducing the residual stresses on the printed layers.Furthermore, holding the printed layers at the annealing temperature(e.g., within annealing window 84) also anneals the successively-printedprinted layers, allowing them to cool down and solidify slowly, whichcan relieve the residual stresses typically associated with amorphousmaterials.

In other words, the part material is preferably supercooled quickly fromits extrusion temperatures down to an annealing temperature in annealingwindow 84, and then held within annealing window 84 for a suitableduration to relieve the residual stresses. After that, the printedlayers of the part material may be cooled down further (e.g., below itsglass transition temperature T_(g) and/or its solidificationtemperature).

Another interesting property of the part materials of the presentdisclosure is that, despite the minimized or reduced crystallinity, thecrystallization that does occur during the supercooling generates asufficient amount of heat to induce extra or increased molecularreptation at the extrudate-part interface. In other words, the heatproduced during the limited crystallization-exothermic reaction allowsthe polymer molecules at the extrudate-part interface to move and becomehighly entangled. It has been observed that, due to the heat of fusionof the extruded roads, the rate of temperature decay of the extrudedpart material can change, and cool down at a slower rate. For example,in an interior raster pattern, this can result in an interfacialtemperature boost, causing better reptation in the X-Y build plane, aslong as the rastered roads contact each other before the extruded partmaterial cools down to the annealing temperature in chamber 12. Thisaccordingly increases the strength of the printed 3D part 30 in both theintra-layer x-y directions, and also in the interlayer z-direction. As aresult, 3D part 30 may have mechanical properties (e.g., strengths andductilities) similar to those of semi-crystalline polymer(s).

Once the printing operation is completed, 3D part 30 may then be cooleddown to room temperature and optionally undergo one or morepost-printing processes. Alternatively, 3D part 30 may be reheated in apost-printing crystallization step. In this step, 3D part 30 may beheated up to about its cold crystallization temperature T_(c,cold) for asufficient duration to induce further crystallization of thesemi-crystalline polymer(s). Examples of suitable annealing durations inthe post-printing crystallization step range from about 30 minutes to 3hours, and may vary depending on the dimensions of each 3D part 30 andthe part material compositions. Correspondingly, examples of suitableannealing temperatures in the post-printing crystallization step rangefrom about the cold crystallization temperature T_(c,cold) of the partmaterial to within about 10° C. above its cold crystallizationtemperature T_(c,cold), and more preferably to within about 5° C. aboveits cold crystallization temperature T_(c,cold).

The post-printing crystallization step can further increase themechanical, thermal, and chemical resistance properties of 3D part 30due to the increased formation of the crystalline regions. Additionally,this post-printing crystallization step is performed on 3D part 30 as awhole (i.e., congruent crystallization), rather than as the layers areindividually printed. As such, any potential shrinkage on 3D part 30from the formation of the crystalline regions occurs in a uniform mannersimilar to the effects in an injection molding process, rather than in alayer-by-layer manner that can otherwise result in curling effects.Another important feature with the post-printing crystallization step isthat 3D part 30 is preferably de-coupled from platen 14 (e.g., from abuild sheet of platen 14), allowing 3D part 30 to be furthercrystallized without being restricted by any non-shrinkable build sheet.

As mentioned above, a 3D part 30 having a translucent, substantiallynon-opaque appearance is an indication that crystallinity has beenretarded during the printing operation. Similarly, the transformationfrom the translucent, substantially non-opaque appearance to an opaqueappearance is an indication that the part material of 3D part 30 hasundergone significant crystallization in the post-printingcrystallization step. After the post-printing crystallization step iscompleted, the resulting 3D part 30 may then be cooled down to roomtemperature and optionally undergo one or more post-printing processes.

The post-printing crystallization step may be performed in chamber 12 ofsystem 10, or alternatively in a separate annealing oven. A separateannealing oven may be preferred in many situations, such as when supportstructure 32 needs to be removed prior to the post-printing annealingstep and/or when system 10 needs to be used for subsequent printingoperations. For example, a printing farm of multiple systems 10 mayoperate in coordination with one or more separate annealing ovens tomaximize the duty cycles of the systems 10.

The above-discussed control of the crystallization kinetics of the partmaterial requires the part material to have a blend of one or moresemi-crystalline polymers and one or more secondary materials,preferably amorphous polymer(s), that retard crystallization of thesemi-crystalline polymer(s) and that are at least partially miscible (ormore preferably, substantially miscible) with the semi-crystallinepolymer(s).

Preferably the semi-crystalline polymer(s) and the secondary material(s)in the blend are separate compounds (e.g., separate polymers) that arehomogenously blended. However, in alternative (or additional)embodiments, part material may include one or more copolymers havingchain segments corresponding to the semi-crystalline polymer(s) and thesecondary material(s), where the chain segments of the secondarymaterial(s) retard the crystallization of the chain segments of thesemi-crystalline polymeric material(s).

In a first embodiment, the part material is a polyamide part materialthat compositionally includes a polyamide blend of one or moresemi-crystalline polyamides, one or more amorphous polyamides, andoptionally, one or more additives dispersed in the polyamide blend. Thesemi-crystalline polyamide(s) may include polyamide homopolymers andcopolymers derived from monomers that include caprolactam, diamines incombination with monomers that include dicarboxylic acids, and mixturesthereof. The diamine monomers and the dicarboxylic acid monomers areeach preferably aliphatic monomers, and more preferably are each acyclicaliphatic monomers.

However, in other embodiments, the diamine monomers and/or thedicarboxylic acid monomers may include aromatic or cycloaliphatic groupswhile maintaining crystalline domains. Furthermore, in some embodiments,the semi-crystalline polyamide(s) may include cyclic groups in graftedpendant chains (e.g., maleated groups), as discussed below. Preferredpolyamide homopolymers and copolymers for the semi-crystallinepolyamide(s) may be represented by the following structural formulas:

where R₁, R₂, and R₃ may each be a hydrocarbon chain having 3-12 carbonatoms. The hydrocarbon chains for R₁, R₂, and R₃ may be branched (e.g.,having small alkyl groups, such as methyl groups) or unbranched, andwhich are preferably aliphatic, acyclic, saturated hydrocarbon chains.

As used herein, reference to a repeating unit identifier “n” in apolymer structural formula means that the bracketed formula repeats forn units, where n is a whole number that may vary depending on themolecular weight of the given polymer. Furthermore, the particularstructures of the bracketed formulas may be the same between therepeating units (i.e., a homopolymer) or may be vary between therepeating units (i.e., copolymer). For example, in the above-shownFormula 1, R₁ may be the same structure for each repeating unit toprovide a homopolymer, or may be two or more different structures thatrepeat in an alternating copolymer manner, a random copolymer manner, ablock copolymer manner, a graft copolymer manner (as discussed below),or combinations thereof.

Preferred polyamides for the semi-crystalline polyamide(s) includenylon-type materials such as polycarpolactum (PA6),polyhexamethyleneaidpamide (PA6,6), polyhexamethylenenonamide (PA6,9),polyhexamethylenesebacamide (PA6,10), polyenantholactum (PA7),polyundecanolactum (PA11), polylaurolactam (PAl2), and mixtures thereof.More preferably, the polyamides for the semi-crystalline polyamide(s)include PA6; PA6,6; and mixtures thereof. Examples of suitablesemi-crystalline polyamide(s) having aromatic groups includesemi-crystalline polyamides of aliphatic diamines and isophthalic acidand/or terephthalic acid (e.g., semi-crystalline polyphthalamides).

Furthermore, in some embodiments, at least a portion of thesemi-crystalline polyamide(s) are graft semi-crystalline polyamide(s),each having a polyamide backbone and one or more impact modifiersgrafted to the backbone. The impact modifiers may includepolyolefin-chain monomers and/or elastomers having coupling groupsconfigured to graft the monomers to the polyamide backbone. Suitablecoupling groups for the impact modifiers include piperidine groups,acrylic/methacrylic acid groups, maleic anhydride groups, epoxy groups.

Preferred coupling groups include maleic anhydride groups and epoxygroups, such as those respectively represented by the followingstructural formulas:

where R₄ and R₅ may each be a hydrocarbon chain having 2-20 carbonatoms, and more preferably 2-10 carbon atoms; and where R₆ may be ahydrocarbon chain having 1-4 carbon atoms. The hydrocarbon chains of R₄,R₅, and R6 may each be branched or unbranched. For example, preferredimpact modifiers include maleated polyethylenes, maleatedpolypropylenes, and mixtures thereof. In embodiments in which the impactmodifier includes an elastomer, preferred impact modifiers includemaleated ethylene propylene diene monomers (EPDM).

Examples of suitable commercial impact modifiers include those availableunder the tradenames LOTADER from Arkema Inc., Philadelphia, Pa.; thoseunder the tradename ELVALOY PTW, FUSABOND N Series, and NUCREL from E.I. du Pont de Nemours and Company, Wilmington, Del.; and those under thetradename ROYALTURF from Chemtura Corporation, Philadelphia, Pa.Examples of preferred graft semi-crystalline polyamides include thosecommercially available under the tradename ULTRAMID from BASFCorporation, Florham Park, N.J.; and those under the tradename GRILAMIDfrom EMS-Chemie, Inc., Sumter, S.C. (business unit of EMS-Grivory).

The grafted impact modifiers may constitute from about 1% to about 20%by weight of the graft semi-crystalline polyamide(s). In someembodiments, the grafted impact modifiers constitute from about 5% toabout 15% by weight of the graft semi-crystalline polyamide(s). Inembodiments that incorporate the graft semi-crystalline polyamide(s),the graft semi-crystalline polyamide(s) may constitute from about 50% to100% by weight of the semi-crystalline polyamide(s) in the partmaterial, more preferably from about 80% to 100% by weight, and evenmore preferably from about 95% to 100% by weight. In some preferredembodiments, the semi-crystalline polyamide(s) of the PA materialconsist essentially of the graft semi-crystalline polyamide(s).

The semi-crystalline polyamide(s) preferably have a molecular weightrange that renders them suitable for extrusion from print head 18, whichmay be characterized by their melt flow indices. Preferred melt flowindices for the semi-crystalline polyamide(s) range from about 1 gram/10minutes to about 40 grams/10 minutes, more preferably from about 3grams/10 minutes to about 20 grams/10 minutes, and even more preferablyfrom about 5 grams/10 minutes to about 10 grams/10 minutes where themelt flow index, as used herein, is measured pursuant to ASTM D1238-10with a 2.16 kilogram weight at a temperature of 260° C.

The PA material also compositionally includes one or more amorphouspolyamides that are preferably miscible with the semi-crystallinepolyamide(s). The amorphous polyamide(s) may include polyamidehomopolymers and copolymers derived from monomers that include diaminesin combination with monomers that include dicarboxylic acids, which arepreferably cycloaliphatic and/or aromatic monomers. However, in otherembodiments, the diamine monomers and/or the dicarboxylic acid monomersmay include aliphatic groups (e.g., acyclic aliphatic groups) whilemaintaining amorphous properties.

Preferred polyamide homopolymers and copolymers for the amorphouspolyamide(s) may be represented by the following structural formulas:

where R₇ and R₁₀ may each be a hydrocarbon chain having 3-12 carbonatoms. The hydrocarbon chains for R₇ and R₁₀ may be branched (e.g.,having small alkyl groups, such as methyl groups) or unbranched, andwhich are preferably aliphatic, acyclic, saturated hydrocarbon chains.In comparison, R₈, R₉, R₁₁, and R₁₂ may each be a hydrocarbon chainhaving 5-20 carbon atoms, which may be branched (e.g., having alkylgroups, such as methyl groups) or unbranched, and each of which includesone or more aromatic groups (e.g., benzene groups), one or morecycloaliphatic groups (e.g., cyclohexane groups), or combinationsthereof.

Preferred polyamides for the amorphous polyamide(s) include nylon-typematerials such as polyamides of hexamethylenediamine, isophthalic acid,terephthalic acid, and adipic acid (PA6i/6T); polyamides of PA2;3,3-dimethyl-4,4-diaminodicyclohexylmethane, and isophthalic acid(PA12/MACMI); polyamides of PA12;3,3-dimethyl-4,4-diaminodicyclohexylmethane, and terephthalic acid(PA12/MACMT); (PA12/MACMI/MACMT); PA6i; PA12/MACM36; PANDT/INDT;polyamides of trimethylhexamethylenediamine and terephthalic acid(PA6/3T); polyamides of cycloaliphaticdiamine and dodecanedioic acid;amorphous polyamides of aliphatic diamines and isophthalic acid and/orterephthalic acid (e.g., amorphous polyphthalamides); and mixturesthereof. More preferably, the polyamides for the amorphous polyamide(s)include PA6/3T, polyamides of cycloaliphaticdiamine and dodecanedioicacid, and mixtures thereof.

In some embodiments, at least a portion of the amorphous polyamide(s)may be graft amorphous polyamide(s), each having a polyamide backboneand one or more impact modifiers grafted to the backbone. Preferredimpact modifiers for grafting to the amorphous polyamide(s) includethose discussed above for the graft semi-crystalline polyamide(s), suchas polyolefin-chain monomers and/or elastomers having coupling groupsconfigured to graft the monomers to the polyamide backbone (e.g.,piperidine groups, acrylic/methacrylic acid groups, maleic anhydridegroups, and epoxy groups). Suitable concentrations of the grafted impactmodifiers in the graft amorphous polyamide(s), and suitableconcentrations of the graft amorphous polyamides relative to theentirety of amorphous polyamide(s) in the part material include thosediscussed above for the graft semi-crystalline polyamide(s).

Preferred concentrations of the amorphous polyamide(s) in the polyamideblend range from about 30% to about 70% by weight, more preferably fromabout 40% to about 60% by weight, and even more preferably from about45% to about 55% by weight, where the semi-crystalline polyamide(s)constitute the remainder of the polyamide blend. Accordingly, preferredratios of the amorphous polyamide(s) to the semi-crystallinepolyamide(s) range from about 3:7 to about 7:3, more preferably fromabout 4:6 to about 6:4, and even more preferably from about 4.5:5.5: toabout 5.5:4.5.

In a second embodiment, the part material includes a substantiallymiscible blend of one or more polyetherimides (PEI) and one or moresemi-crystalline polyaryletherketones (PAEK), such as one or morepolyetherketones (PEK), polyetheretherketones (PEEK),polyetherketoneketones (PEKK), polyetheretherketoneketones (PEEKK),polyetherketoneether-ketoneketones (PEKEKK), mixtures thereof, and thelike, and more preferably one or more polyetheretherketones (PEEK).Preferred concentrations of the polyaryletherketone(s) in this blendrange from about 35% by weight to about 99% by weight, and morepreferably from about 50% by weight to about 90% by weight, and evenmore preferably form about 60% by weight to about 80% by weight, wherethe polyetherimide(s) constitute the remainder of the blend.

In a third embodiment, the part material includes a substantiallymiscible blend of one or more polyphenylsulfones (PPSU), polysulfones(PSU), and/or polyethersulfones (PES), with one or more semi-crystallinepolyaryletherketones. Preferred concentrations of thepolyphenylsulfone(s)/polysulfone(s)/polyethersulfone(s) in this blendrange from about 1% by weight to about 65% by weight, and morepreferably from about 20% by weight to about 50% by weight, where thepolyaryletherketone(s) constitute the remainder of the blend.

In a fourth embodiment, the part material includes a substantiallymiscible blend of one or more polycarbonates and one or moresemi-crystalline polybutylene terephthalates (PBT) and/or one or moresemi-crystalline polyethylene terephthalates (PET). Preferredconcentrations of the polycarbonate(s) in this blend range from about30% by weight to about 90% by weight, and more preferably from about 50%by weight to about 70% by weight, where the polybutyleneterephthalate(s)/polyethylene terephthalate(s) constitute the remainderof the blend.

In a fifth embodiment, the part material includes a substantiallymiscible blend of one or more amorphous polyethylene terephthalates(e.g., glycol-modified polyethylene terephthalates) and one or moresemi-crystalline polyethylene terephthalates. Preferred concentrationsof the amorphous polyethylene terephthalate(s) in this blend range fromabout 10% by weight to about 40% by weight, and more preferably fromabout 15% by weight to about 25% by weight, where the semi-crystallinepolyethylene terephthalate(s) constitute the remainder of the blend.

In a sixth embodiment, the part material includes a substantiallymiscible blend of one or more amorphous polyaryletherketones and one ormore semi-crystalline polyaryletherketones, such as one or moreamorphous polyetherketoneketones (PEKK) and one or more semi-crystallinepolyetherketoneketones (PEKK). Preferred concentrations of the amorphouspolyaryletherketones(s) in this blend range from about 30% by weight toabout 90% by weight, and more preferably from about 50% by weight toabout 70% by weight, where the semi-crystalline polyaryletherketones(s)constitute the remainder of the blend.

In some embodiments, the part material may also include additionaladditives, such as colorants, fillers, plasticizers, impact modifiers,and combinations thereof. In embodiments that include colorants,preferred concentrations of the colorants in the part material rangefrom about 0.1% to about 5% by weight. Suitable colorants includetitanium dioxide, barium sulfate, carbon black, and iron oxide, and mayalso include organic dyes and pigments.

In embodiments that include fillers, preferred concentrations of thefillers in the part material range from about 1% to about 45% by weightfor some fillers (e.g., glass and carbon fillers), and up to about 80%by weight for other fillers, such as metallic and ceramic fillers.Suitable fillers include calcium carbonate, magnesium carbonate, glassspheres, graphite, carbon black, carbon fiber, glass fiber, talc,wollastonite, mica, alumina, silica, kaolin, silicon carbide, zirconiumtungstate, soluble salts, metals, ceramics, and combinations thereof.

In the embodiments including the above-discussed additional additives,the polymer blend preferably constitutes the remainder of the partmaterial. As such, the polymer blend may constitute from about 55% to100% by weight of the part material, and more preferably from about 75%to 100% by weight. In some embodiments, the polymer blend constitutesfrom about 90% to 100% by weight of the part material, more preferablyfrom about 95% to 100% by weight. In further embodiments, the partmaterial consists essentially of the polymer blend, and optionally, oneor more colorants and/or anti-oxidants.

Preferably, the polymer blend is also substantially homogenous, allowingeach portion of the part material used in an additive manufacturingsystem to consistently exhibit the same thermal and physical properties.For example, with system 10 having print head 18, the flow rate of themolten part material (i.e., melt 70) from nozzle 48 is controlled by therate at which filament 52 enters liquefier tube 56, and the melting rateof filament 52 within heating zone 68. System 10 may operate with presetinstructions for extruding melt 70 at desired flow rates based on toolpath geometries. These preset instructions are preferably based on thethermal properties of the part material, namely the melting rate andviscosity of the part material, as well as the crystallization kineticsof the part material.

As such, if the polymer blend were otherwise non-homogenous, the partmaterial would not be uniform. This could cause successive segments offilament 52 to melt at different rates, affecting the height of meniscus74. This accordingly can change the extrusion rate of melt 70 from thepreset instructions, which can impair part quality in 3D part 30.Additionally, a non-homogenous blend may result in imbalances in thecrystallization kinetics of the part material, which could reduce theabove-discussed benefits of controlling the crystallization kinetics.Accordingly, filament 52 is preferably manufactured from a part materialhaving a substantially homogenous polymer blend of the semi-crystallinepolymer(s) and the secondary material(s) (e.g., amorphous polymer(s)).In embodiments that include one or more additives, the additive(s) arepreferably dispersed in the polymer blend in a substantially uniformmanner.

As mentioned above, the above-discussed method may also be utilized withelectrophotography-based additive manufacturing systems and selectivelaser sintering systems. With respect to electrophotography-basedadditive manufacturing systems, the part material may be provided inpowder form for use in an electrophotography-based additivemanufacturing system, such as those disclosed in Hanson et al., U.S.Publication Nos. 2013/0077996 and 2013/0077997, and Comb et al., U.S.Publication Nos. 2013/0186549 and 2013/0186558, the disclosures of whichare incorporated by reference to the extent that they do not conflictwith the present disclosure.

As discussed in these references, the electrophotography-based additivemanufacturing systems preferably operate with layer transfusionassemblies that transfuse each successively-developed layer based oninterlayer polymer entanglement (i.e., reptation). As such, theabove-discussed method for controlling the crystallization kinetics ofthe part material for the extrusion-based additive manufacturing systemsmay also be used in the same manner with the electrophotography-basedadditive manufacturing systems.

In comparison, however, selective laser sintering systems may print 3Dparts from nylon materials in a manner in which a nylon material is heldin a gelatinous, undercooled amorphous state between the meltingtemperature and the hot crystallization temperature of the nylonmaterial. However, nylon materials typically have small temperaturewindows between their melting temperatures and the hot crystallizationtemperatures, rendering it difficult to hold the printed layers in thisamorphous state after being melted with a laser beam.

However, as discussed above, it has been found that the substantiallymiscible blends for the part material of the present disclosure decreasethe hot crystallization temperature T_(c,hot) of the part material fromthat of the semi-crystalline polymer(s). Conversely, the meltingtemperature T_(m) of the part material remains substantially unchanged.As such, the substantially miscible blend for the part material widensthe operating window, referred to as operating window 88 in FIG. 4, inwhich the printed layers may be held in the gelatinous, undercooledamorphous state to prevent warping and distortions. In this case, thepowder materials may be selectively melted with the laser beam and heldwithin this operating window 88 until the printing operation iscompleted. The whole 3D part 30 may then be cooled down in aconventional manner.

In embodiments involving the above-discussed technique used in aselective laser sintering system (e.g., systems disclosed in Deckard,U.S. Pat. Nos. 4,863,538 and 5,132,143), the part material may beprovided in powder form for use in other powder-based additivemanufacturing systems. In some alternative embodiments, such as withsome polyamide materials (e.g., glass-filled PA6/10 materials), thistechnique may also be utilized in extrusion-based and/orelectrophotography-based additive manufacturing systems. This canaccordingly produce 3D parts having high heat deflection temperatures,which can be beneficial for use with soluble support materials.

EXAMPLES

The present disclosure is more particularly described in the followingexamples that are intended as illustrations only, since numerousmodifications and variations within the scope of the present disclosurewill be apparent to those skilled in the art. Unless otherwise noted,all parts, percentages, and ratios reported in the following examplesare on a weight basis, and all reagents used in the examples wereobtained, or are available, from the chemical suppliers described below,or may be synthesized by conventional techniques.

I. Examples 1-4

Part materials of Examples 1-4 and Comparative Examples A and B wereprepared as PEEK/PEI blends with varying weight ratios. Each partmaterial was then analyzed using DSC to determine the glass transitiontemperature T_(g), cold crystallization temperature T_(c,cold), meltingtemperature T_(m), and hot crystallization temperature T_(c,hot). Table1 lists the DSC results for the tested part materials with the PEEK/PEIratios, where the temperatures were reported in degrees Celsius.

TABLE 1 PEEK/PEI Weight T_(c, cold) T_(m) T_(c, hot) Example Ratio T_(g)(peak) (peak) (peak) Comparative Example A 100/0  146 — 346 303 Example1 85/15 160 207 341 288 Example 2 70/30 179 249 338 265 Example 3 55/44181 265 337 266 Example 4 35/65 191 — 338 — Comparative Example B  0/100214 — — —

The results in Table 1 show the relative changes in the glass transitiontemperature T_(g), cold crystallization temperature T_(c,cold), meltingtemperature T_(m), and hot crystallization temperature T_(c,hot) for thedifferent PEEK/PEI ratios. For example, the glass transition temperatureT_(g) increases substantially with the increased concentration of PEI.Furthermore, the cold crystallization temperature T_(c,cold) and the hotcrystallization temperature T_(c,hot) converged closer together with theincreased concentration of PEI, but the melting temperature T_(m)remained relatively the same (e.g., 4 degree drop between Examples 1 and3, versus a 22 degree drop for the hot crystallization temperatureT_(c,hot)).

Accordingly, the differences between the glass transition temperaturesT_(g) and the cold crystallization temperatures T_(c,cold) for Examples1-3 provide suitable annealing windows (e.g., annealing window 84) forprinting 3D parts with extrusion-based and/or electrophotography-basedadditive manufacturing systems. Similarly, the differences between themelting temperatures T_(m) and the hot crystallization temperatureT_(c,hot) for Examples 1-3 provide suitable operating windows (e.g.,operating window 88) for printing 3D parts with selective lasersintering systems.

The DSC testing also involved reheating the part materials after thecooling step to simulate a post-printing crystallization step. Duringthis reheating step, the part materials of Examples 2 and 3 eachexhibited two different glass transition temperatures T_(g). The partmaterial of Example 2 had a first glass transition temperature of 164°C. and a second glass transition temperature of 209° C. The partmaterial of Example 2 had a first glass transition temperature of 167°C. and a second glass transition temperature of 210° C. This phenomenonis believed to be caused by the PEEK and PEI polymers separating uponcrystallization, such that the PEI was not incorporated in the PEEKcrystalline regions.

The enthalpy of fusions at the hot crystallization temperature T_(c,hot)for the part materials were also determined, as listed below in Table 2.

TABLE 2 PEEK/PEI Enthalpy of Weight Fusion Example Ratio (Joules/gram)Comparative Example A 100/0  56 Example 1 85/15 43 Example 2 70/30 37Example 3 55/44 37 Example 4 35/65 3 Comparative Example B  0/100 —

The results in Table 2 show that the part materials of Examples 1-3exhibit high levels of exothermic energy upon crystallization. The partmaterial of Example 4 appeared to generate very little crystallization.However, this is believed to be due to a kinetic phenomenon that woulddisappear with slower cooling. The part material of Example 4 exhibiteda melting point (as shown above in Table 1) and turned opaque uponreheating (i.e., re-crystallization).

II. Example 5

A part material of Example 5 having a PEEK/PEI weight ratio of 60/40 wascompounded into cylindrical filaments having an average diameter ofabout 0.07 inches and wound onto spools of consumable assemblies. Foreach run, the consumable assembly was loaded to an extrusion-basedadditive manufacturing system commercially available from Stratasys,Inc., Eden Prairie, Minn. under the trademarks “FDM” and “FORTUS 400mc”.The filament was then fed from the consumable assembly to print headliquefier assembly of the system, melted, and extruded from print headnozzle to print 3D parts in a heated chamber maintained at 160° C.(i.e., below its glass transition temperatures T_(g)).

FIG. 5 illustrates pellets and the printed 3D parts from the partmaterial of Example 5. The printed 3D part and associated pelletsexhibited a golden, translucent appearance due to the low levels ofcrystallinity. A corresponding 3D part and portions of the pellets werealso reheated to about 200° C. (i.e., a post-printing crystallizationprocess) for a sufficient duration to re-crystallize the PEEK in thepart material. As shown, the annealed 3D part and pellets each exhibitedan opaque appearance, which was more tan/whitish in color than thegolden color of the non-re-crystallized part/pellets.

III. Example 6

Part materials of Example 6 were prepared as polyamide blends, where thesemi-crystalline polyamide was a graft PA12 polyamide commerciallyavailable under the tradename GRILAMID L16 from EMS-Chemie, Inc.,Sumter, S.C. (business unit of EMS-Grivory), and the amorphous polyamidewas a PA12 polyamide commercially available under the tradename GRILAMIDTR90 from EMS-Chemie, Inc., Sumter, S.C. (business unit of EMS-Grivory).

For each part material of Example 6, the semi-crystalline polyamideconcentration in the part material ranged from 27.2%-28.2% by weight,and the amorphous polyamide concentration in the part material rangedfrom 65.2%-66.2% by weight, for a blend ratio of about 70:30 of theamorphous polyamide to semi-crystalline polyamide. The part materialalso included an impact modifier having a concentration in the partmaterial ranging from 4.5%-5.5% by weight, and an anti-oxidant having aconcentration in the part material ranging from 0.03%-0.13% by weight.

Each part material of Example 6 was analyzed using DSC to provide anaverage glass transition temperature T_(g) of 55° C., an average coldcrystallization temperature T_(c,cold) of 130° C., an average meltingtemperature T_(m) of 178° C., and an average hot crystallizationtemperature T_(c,hot) of 148° C. Each part material was also compoundedinto cylindrical filaments having an average diameter of about 0.07inches and wound onto spools of consumable assemblies.

For each run, the consumable assembly was loaded to an extrusion-basedadditive manufacturing system commercially available from Stratasys,Inc., Eden Prairie, Minn. under the trademarks “FDM” and “FORTUS 400mc”.The liquefier temperature was set to 355° C. and the heated chambertemperature was set to 80° C., 100° C., or 120° C., depending on the 3Dpart geometry being printed. Each 3D part exhibited good dimensionalstability and low levels of crystallinity.

IV. Examples 7 and 8

A part materials of Example 7 was prepared as an impact-modified PETblend, where the semi-crystalline PET was a polyethylene terephthalatecopolymer commercially available under the tradename “SKYPET BR” from SKChemicals, South Korea, and the amorphous PET was a glycol-modifiedpolyethylene terephthalate commercially available under the tradename“SKYGREEN S2008” from SK Chemicals, South Korea. The part materialincluded 76% by weight of the semi-crystalline PET, 19% by weight of theamorphous PET, and 5% by weight of an impact modifier commerciallyavailable under the tradename “ELVALOY PTW” from E.I. du Pont de Nemoursand Company, Wilmington, Del.

The part material of Example 7 was compounded into cylindrical filamentshaving an average diameter of about 0.07 inches and wound onto spools ofconsumable assemblies. For each run, the consumable assembly was loadedto an extrusion-based additive manufacturing system commerciallyavailable from Stratasys, Inc., Eden Prairie, Minn. under the trademarks“FDM” and “FORTUS 400mc”.

During the printing operations, the filament was melted and extrudedfrom a print head at a temperature of 320° C. into a heated buildchamber, where the temperature of the build chamber was held at 90° C.,100° C., 110° C., and 120° C. for four different runs. The part materialhad a glass transition temperature of about 78° C. As such, thesedifferent temperatures tested how the different annealing windowsaffected the level of crystallinity in the resulting 3D part.

After being printed, each of the four 3D parts was slowly heated and theresulting modulus was measured, as illustrated in FIG. 6. As shown inFIG. 6, the part material annealed at 90° C. maintained amostly-amorphous mechanical behavior, while the part material annealedat 120° C. maintained a mostly-semi-crystalline mechanical behavior. Thepart materials annealed at 100° C. and 110° C. fell between these twoend points.

As can be seen, over a heated chamber temperature range of about 30degrees Celsius, the dynamic mechanical behavior of the tested partmaterials changed significantly from almost mostly amorphous to almostmostly crystalline. This is further illustrated by the tan-delta peakonset in FIG. 7, where the peak onset occurred later as the temperaturein the heated chamber increased, which corresponded to a morecrystalline 3D part. Accordingly, these results confirm that the extentof crystallization in the resulting 3D part for the part materials canbe controlled by a properly-selected annealing window.

The part material of Example 8 included 70% by weight of the PET blendof Example 7 and 30% by weight of a glass-based filler. The partmaterial of Example 8 was also printed as discussed above for the partmaterials of Example 6, where the heated chamber was held at only 80° C.to maintain a mostly-amorphous mechanical behavior. A portion of the 3Dpart samples were then reheated to about 135° C. (i.e., a post-printingcrystallization process) for a sufficient duration to re-crystallize thesemi-crystalline PET in the part material.

After being printed, each 3D part sample was then slowly heated and theresulting modulus was measured, as illustrated in FIG. 8, which alsocompares the results of the part material for Example 7 printed in the120° C. heated chamber. As shown in FIG. 8, the post-printingcrystallization process significantly increased the crystallinity of thepart material compared to the initial samples.

Although the present disclosure has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the disclosure.

The invention claimed is:
 1. A method for printing a three-dimensionalpart with an additive manufacturing system, the method comprising:providing a part material compositionally including one or moresemi-crystalline polymers and one or more secondary materials that areconfigured to retard crystallization of the one or more semi-crystallinepolymers, wherein the one or more secondary materials are substantiallymiscible with the one or more semi-crystalline polymers; melting thepart material in the additive manufacturing system; forming at least aportion of a layer of the three-dimensional part from the melted partmaterial in a build environment; and maintaining the build environmentat an annealing temperature that is between a glass transitiontemperature of the part material and a cold crystallization temperatureof the part material.
 2. The method of claim 1, wherein the one or moresecondary materials comprise one or more amorphous polymers.
 3. Themethod of claim 2, wherein the one or more amorphous polymers constitutefrom about 50% by weight to about 85% by weight of a combined weight ofthe one or more semi-crystalline polymers and the one or more amorphouspolymers.
 4. The method of claim 1, wherein the one or moresemi-crystalline polymers comprise one or more semi-crystallinepolyamides, and wherein the one or more secondary materials comprise oneor more amorphous polyamides.
 5. The method of claim 1, wherein the oneor more semi-crystalline polymers comprise one or more one or morepolyaryletherketones, and wherein the one or more secondary materialscomprise one or more polyetherimides.
 6. The method of claim 1, andfurther comprising performing a post-printing crystallization step onthe printed three-dimensional part.
 7. The method of claim 1, whereinthe one or more semi-crystalline polymers are polymerized from one ormore base monomers, and wherein the one or more secondary materialscomprise one or more second semi-crystalline polymers polymerized fromone or more monomers that are isomers of the one or more base monomers.8. The method of claim 7, wherein the one or more semi-crystallinepolymers and the one or more second semi-crystalline polymers eachcomprise one or more polylactic acid polymers, one or morepolyetherketoneketone polymers, or one or more polyesters.
 9. A methodfor printing a three-dimensional part from with an additivemanufacturing system, the method comprising: providing a part materialthat compositionally comprises one or more semi-crystalline polymers andone or more amorphous polymers that are substantially miscible with theone or more semi-crystalline polymers; maintaining a build environmentof the additive manufacturing system, at least in a deposition region ofthe build environment, at an annealing temperature that is between aglass transition temperature of the part material and a coldcrystallization temperature of the part material; feeding the partmaterial to a print head retained by of the additive manufacturingsystem; melting the part material in the print head; extruding themelted part material from the print head; and depositing the extrudedpart material onto a build surface in the deposition region to form atleast a portion of a layer of the three-dimensional part from theextruded part material.
 10. The method of claim 9, wherein the one ormore semi-crystalline polymers comprise one or more semi-crystallinepolyamides, and wherein the one or more amorphous polymers comprise oneor more amorphous polyamides.
 11. The method of claim 10, wherein theone or more amorphous polymers constitute from about 50% by weight toabout 85% by weight of a combined weight of the one or moresemi-crystalline polymers and the one or more amorphous polymers. 12.The method of claim 8, and further comprising selecting the annealingtemperature to achieve a predetermined crystallinity level for the partmaterial of the printed three-dimensional part.
 13. The method of claim8, wherein the one or more amorphous polymers are configured to retardcrystallization of the one or more semi-crystalline polymers.
 14. Themethod of claim 8, and further comprising performing a post-printingcrystallization step on the printed three-dimensional part.
 15. A methodfor printing a three-dimensional part with an additive manufacturingsystem, the method comprising: providing a part material thatcompositionally comprises one or more semi-crystalline polymers and oneor more amorphous polymers that are substantially miscible with the oneor more semi-crystalline polymers; melting the part material in theadditive manufacturing system; forming layers of the three-dimensionalpart from the melted part material using an additive manufacturingtechnique, wherein the layers are formed in a region that is maintainedat an annealing temperature that is within 10° C. of a glass transitiontemperature of the part material; and reheating the printedthree-dimensional part to one or more temperatures that are within about10° C. of a cold crystallization temperature of the part material. 16.The method of claim 15, wherein a re-crystallization temperature iswithin about 5° C. of the cold crystallization temperature of the partmaterial.
 17. The method of claim 15, wherein reheating the printedthree-dimensional part to the one or more temperatures is performed forat least about 30 minutes.
 18. The method of claim 15, wherein thereheating step is performed in a separate oven from the additivemanufacturing system.
 19. The method of claim 18, and further comprisingseparating the three-dimensional part from a build sheet used toreceived the formed layers of the three-dimensional part.
 20. The methodof claim 15, wherein the one or more semi-crystalline polymers compriseone or more semi-crystalline polyamides, and wherein the one or moreamorphous polymers comprise one or more amorphous polyamides.